In general, a film forming process for forming a desired thin film on a semiconductor wafer, an LCD substrate or the like and a pattern etching process for etching a desired pattern thereon are repeatedly performed to manufacture an integrated circuit (IC) or a logic device.
For example, in the case of the film forming process, a silicon thin film, a silicon oxide thin film, a silicon nitride thin film, a metal thin film, a metal oxide thin film, a metal nitride thin film or the like is formed on the surface of a target substrate to be processed by allowing a predetermined processing gas (source gas) to react in the processing chamber. As such, when such film forming reaction is performed, residual reaction byproducts are produced and exhausted along with the exhaust gas. Further, an unreacted processing gas is also exhausted.
If the reaction byproducts and the unreacted processing gas are exhausted to the atmosphere as they are, they cause an environmental pollution. In order to prevent such environmental pollution, a trap mechanism is typically provided in a gas exhaust system extended from the processing chamber to trap and remove the reaction byproducts, the unreacted processing gas and the like included in the exhaust gas.
The configuration of the trap mechanism is varied depending on the properties of the reaction byproducts or the like to be trapped and removed. For example, in the case of removing the reaction byproducts that are condensed (liquefied) or coagulated (solidified) at a room temperature, the trap mechanism has, e.g., a configuration in which a plurality of fins is provided in a casing including an introduction port and an exhaust port of the exhaust gas. The fins are arranged in the direction along which the exhaust gas flows. When the exhaust gas passes between the fins, the reaction byproducts or the like included in the exhaust gas are attached on surfaces of the fins to be trapped and removed.
In this regard, the fins are cooled by a cooling medium or the like to improve the trap efficiency (see, e.g., JP2001-214272A). Further, there has been proposed a recovery method in which a scrubber for scattering water is used as the trap mechanism, and the exhaust gas is contacted with the scattered water so that the reaction byproducts and/or the unreacted gas components are dissolved in the scattered water to be recovered.
There is another trap mechanism in which a detachably disposable cartridge-type absorption tower is provided to absorb therein the reaction byproducts and/or the unreacted gas components to remove them from the exhaust gas. In the trap mechanism, if the removing capacity of the absorption tower is reduced to a predetermined level, the absorption tower is wasted and replaced with a new absorption tower. The reason that the used absorption tower is wasted is because it is relatively difficult to recover a useful metal from the trapped reaction byproducts in case where halogen elements such as fluorine (F), chlorine (Cl) or the like are included in the source gas.
Further, harmful gas components may be included in the gas exhausted from the trap mechanism. The harmful gas components are scrubbed by a scrubbing unit provided at a downstream side (rear end) of the trap mechanism. Then, the exhaust gas is exhausted to the atmosphere.
Recently, a thin film is formed by a film forming device by using an organic metal compound source gas containing a precious metal such as silver, gold, ruthenium or the like in order to reduce the wiring resistance or the contact resistance. Such precious metal is very expensive. Moreover, some of sources of the aforementioned organic metal compound may contain carbon, hydrogen, oxygen and the like in addition to metal atoms but does not contain halogen elements such as F, Cl and the like. Accordingly, if such trap method using a disposable trap unit is employed, the expensive metals are uselessly wasted, causing an increase in the running cost.
For that reason, in, e.g., JP2001-342566A, to improve the effective use of the precious metals or expensive metals, there has been suggested a recover method for trapping reaction byproducts containing an unreacted source by cooling and thus, e.g., condensing the exhaust gas exhausted from the processing gas; and obtaining the unreacted source by refining the reaction byproducts. Since, however, the reaction byproducts and the unreacted source are trapped together in the trap method disclosed in JP2001-342566A, it is necessary to perform the refining process for obtaining the unreacted source thereafter, thereby resulting in the troublesome work.
Further, the conventional scrubber or the trap mechanism using the fins is disadvantageous in that it is required to include a separate scrubbing unit and, thus, its install space becomes increased.